atomic structure

• how has the Dalton model of an atom changed over time?


  Dalton had his own three part atomic theory (1803) :

  • all substances are made of atoms (small particles that cannot be created, divided or destroyed)
  • atoms of the same element are alike, atoms of different elements are different
  • atoms join with other atoms to make new substances

  JJ Thomson (1897)

  • plum pudding model
  • negative electrons were embedded in a positively charged sphere

  Ernest Rutherford (1909)

  • developed a new model
  • most of the atoms mass is found in the centre called the nucleus
• the structure of an atom contains a nucleus (protons and neutrons) surrounded by electrons in shells
• why do atoms contain the same number of electrons and protons?


  • atoms are neutral the the charge of the electron is -1 and the charge of the proton is +1
  • therefore nr of electrons = nr of protons as they need to cancel eachother out
• the nucleus is very small compared to the overall size of the atom, as the nucleus is located inside the atom
• mass number of an atom = nr of protons + nr of neutrons
• atoms of a given element have the same nr of protons in the nucleus and that number is unique to that element
• isotopes are different atoms of the same element with the same number of protons but a different number of neutrons
• how to calculate nr of neutrons, electrons and protons given the mass nr and atomic nr ?


  atomic number = nr of protons , nr of electrons

  mass number - atomic number = nr of neutrons
• isotopes always have the same nr of protons but different nrs of neutrons meaning that the mass number is different, the mass is used by calculating the abundance of of different isotopes and as it is an average it could lead to the mass not being a whole number
• relative atomic mass

  A) 100

  B) mass

  C) %

  
• relative mass and charge of electron , proton and neutron

  A) -1

  B) proton

  C) 0